Bill George is a senior fellow at Harvard Business School and former chairman and CEO of Medtronic.

When I graduated from college, I had the naive notion that the journey to leadership was a straight line to the top. I learned the hard way that leadership is not a singular destination but a marathon journey that progresses through many stages until you reach your peak. I was not alone. Of all the senior leaders we interviewed, none wound up where they thought they would.

Former Vanguard CEO Jack Brennan believes that the worst thing people can do is to manage their careers with a career map: “The dissatisfied people I have known and those who experienced ethical or legal failures all had a clear career plan.” Brennan recommended being flexible and venturesome in stepping up to unexpected opportunities. “If you’re only interested in advancing your career, you’ll wind up dissatisfied,” he said.

The idea of a career ladder places tremendous pressure on leaders to keep climbing ever higher. Instead, Sheryl Sandberg, chief operating officer (COO) of Facebook, favors the idea of a career “jungle gym” where you can move up, down, or across. Realistically, your development as a leader is a journey filled with many ups and downs as you progress to your peak leadership and continue leading through the final stage.

The leader’s journey follows the new span of life, which often runs into the nineties. Individuals move through three periods of leadership with different types of leadership opportunities unfolding in each. There will be differences in the pace at which leaders navigate the timeline, but there are many commonalities among their experiences.

Phase I: Preparing for Leadership

Phase I is preparing for leadership, when character forms and people act as individual contributors or lead teams for the first time. Today, very few leaders make career commitments in their twenties. Increasingly, they use the time following college to gain valuable work experience, oftentimes changing jobs every 18 to 24 months to diversify their experience. Many young leaders are interested in going to graduate school in business, law, or government. Even some whocomplete their master’s degrees prefer individual contributor roles in consulting or finance before committing to a specific company or industry.

There is a natural amount of self-absorption in this phase. Measures of success in your teens and twenties are based primarily on what you accomplish as an individual. Your performance determines what schools you are admitted to and how well you do in your work. Here’s how Kleiner Perkins Caufield & Byers’s Randy Komisar described it:

We begin life on a linear path where success is based on clear targets. Life gets complicated when the targets aren’t clear, and you have to set your own. By rubbing up against the world, you get to know yourself. Either do that, or you’re going to spend your life serving the interests and expectations of others.

He acknowledged that the start of the journey is particularly hard for young people “They look at me and say, ‘Hey, man. All I want to do is to get a good job, buy a house, get married, and have kids.’” Komisar said he wished life were so simple. Instead, he tells them:

Let me just plant this seed. Keep it alive and come back to it in 10 years, but don’t flush it. Ask yourself the question “What do you want out of your life?” I want to empower you for that time when it’s relevant to you.

Wendy Kopp: Stepping Up at 21

As a student at Princeton, Wendy Kopp developed a passion to transform K–12 education. Growing up in a middle-class family in an affluent Dallas suburb, she lived in a community that was “extraordinarily isolated from reality and the disparities in educational opportunity.” Kopp was influenced by her freshman roommate at Princeton, who was from inner-city New York. Kopp described her roommate as brilliant but unable to keep up with her studies because her high school had not prepared her for the rigors of Princeton. Ultimately, her roommate dropped out of school.

As a senior, Kopp burned with desire to transform education but didn’t know how to get there. Not wanting to pursue the typical corporate-training track, she went into “a deep funk.” As she explored teaching, she realized many others also believed that depriving kids of an excellent education was a national tragedy.

So she organized a conference of students and business leaders to examine ways to improve K–12 education. During the conference, an idea came to her: “Why doesn’t this country have a national teacher corps of recent college graduates who commit two years to teach in public schools?” Her rhetorical question inspired her to found Teach For America (TFA), the most successful secondary educational program of the past 25 years.

Kopp’s journey wasn’t easy. Lacking management experience and permanent funding, Teach For America was constantly short of cash, lurching from one crisis to the next. Time and again, Kopp threw herself into fundraising as she restructured budgets and financing to cover deficits. After working 100 hours a week for five years to build TFA to 500 new teachers per year, Kopp felt overwhelmed by the financial pressures of raising money to keep the organization going.

When many initial funders decided not to continue funding the organization, losses mounted to a cumulative deficit of $2.5 million. A blistering critique of TFA in an influential educators’ journal said, “TFA is bad policy and bad education. It is bad for the recruits. It is bad for the schools. It is bad for the children.” Reflecting on the article, Kopp recalled, “It felt like a punch in the chest. I read it more as a personal attack than an academic analysis of our efforts.” When some of her original team left TFA, Kopp thought about shutting it down. “Yet my passion for our cause and fear that we might let the children down kept me going,” she said.

Kopp’s experience at such a young age is the essence of authentic leadership: Find something you are passionate about, and inspire others to join the cause. TFA’s crisis accelerated her development as a leader. Twenty years after founding TFA, Kopp’s tireless efforts and passionate leadership have paid off. Today the program has 11,000 corps members who are teaching more than 750,000 students.

Ian Chan: Creating a Scientific Revolution

Ian Chan is another young leader who discovered his passion to lead at an early age. As his college graduation approached, he knew he wanted “an opportunity that would get me excited to jump out of bed every day and go to work.” After uninspiring experiences in investment banking and private equity, he and his younger brother focused on the human genome revolution.

The Chan brothers founded U.S. Genomics to revolutionize medicine by delivering personalized genomics on a broad scale. They attracted noted advisers, such as scientist Craig Venter, who originally mapped the human genome, and Bob Langer, a renowned technologist. They began with a $100,000 credit card loan, and subsequently raised $52 million from venture capitalists, several of whom joined the board as the Chan brothers gave up more than half their ownership.

Over the next five years the company’s work attracted attention in the scientific community and venture capital world as U.S. Genomics became a pioneer in its field. When the founders presented the company’s exceptional performance in December 2001, the board gave them a standing ovation. Yet, as the full potential of U.S. Genomics became apparent to the venture capitalists, they decided they needed a more experienced executive to lead it. Four months later, Chan was shocked when his board told him he was being replaced as CEO. “To this day, I have no idea why this happened when things were going so well,” he said.

I put my heart and soul into it for many years, and then boom, it’s all gone. It was gut-wrenching to have something taken away that I created and believed in deeply. I still had some shares, but I wasn’t part of the enterprise anymore with its mission I believe in. I wanted to continue fighting, but I felt helpless. In hindsight, it was a rich experience I can build on for the next journey. I had been working crazy hours and was very tired. I didn’t have a personal life and needed more balance. To regroup, I spent two years getting my MBA. That provided time for self-reflection and opportunities to interact with some of the world’s top business leaders.

I realized I was still fortunate to have my health, family, and the privilege of living in a free country. These should never be taken for granted. My heart is still in entrepreneurship and biotechnology because there are so many untreatable diseases that provide opportunities to make broad impact.

Chan was a victim of his own success. Yet for all the heartache and pain, he had an invaluable experience that has been formative on his leadership journey. He and his brother, Eugene, rejoined forces in 2007 to found Abpro, focusing on producing proteins used in life sciences. They raised $1.5 million in seed capital but have retained more than 50 percent ownership to avoid repeating the U.S. Genomics experience. Chan said he learned from these experiences “the importance of pursuing your passion to make scientific breakthroughs” but also “not to give up control to outsiders.”

Unfortunately, fear of failure keeps many young leaders from jumping into opportunities like Kopp and Chan did.

Don’t worry about the challenges. Embrace them. Go through them even if they hurt. Tell yourself, there is something to be learned from this experience. You may not fully understand it now, but you will later. It’s all part of life, and life is a process of learning. Every challenging experience develops your core of inner strength, which gets you through those storms. Nothing worth doing in life is going to be easy.